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Philips Semiconductors
Power stage 2 x 10 or 1 x 20 W class-D
audio amplifier
8
FUNCTIONAL DESCRIPTION
The TDA8928J is a two-channel audio power amplifier
system using class-D technology.
The power stage TDA8928J is used for driving the
loudspeaker load. It performs a level shift from the
low-power digital PWM signal, at logic levels, to a
high-power PWM signal that switches between the main
supply lines. A 2nd-order low-pass filter converts the PWM
signal into an analog audio signal across the loudspeaker.
8.1
Power stage
The power stage contains high-power DMOS switches,
drivers, timing and handshaking between the power
switches and some control logic (see Fig.1).
The following functions are available:
Switch (pins SW1 and SW2): digital inputs; switching
from V
to V
+ 12 V and driving the power DMOS
SS
SS
switches
Release (pins REL1 and REL2): digital outputs;
switching from V
to V
SS
SW2 with a small delay. Note: for self oscillating
applications this pin is not used
Power-up (pin POWERUP): must be connected to a
continuous supply voltage of at least V
respect to V
SS
Enable (pins EN1 and EN2): digital inputs; at a level of
V
the power DMOS switches are open and the PWM
SS
outputs are floating; at a level of V
stage is operational
Diagnostics (pin DIAG): digital open-drain output; pulled
down to V
if the maximum temperature or maximum
SS
current is exceeded.
2004 May 05
+ 12 V; follow pin SW1 and
SS
+ 5 V with
SS
+ 12 V the power
SS
8.2
Protection
Temperature and short-circuit protection sensors are
included in the TDA8928J. The diagnostic output is pulled
down to V
in the event that the maximum current or
SS
maximum temperature is exceeded. The system shuts
itself down when pin DIAG is connected to pins EN1 and
EN2.
8.2.1
M
AXIMUM TEMPERATURE
Pin DIAG becomes LOW if the junction temperature (T
exceeds 150 C. Pin DIAG becomes HIGH again if T
dropped to approximately 130 C, so there is a hysteresis
of approximately 20 C.
8.2.2
M
AXIMUM CURRENT
When the loudspeaker terminals are short-circuited this
will be detected by the current protection. Pin DIAG
becomes LOW if the output current exceeds the maximum
output current of 2 A. Pin DIAG becomes HIGH again if the
output current drops below 2 A. The output current is
limited at the maximum current detection level when pin
DIAG is connected to pins EN1 and EN2.
6
Preliminary specification
TDA8928J
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